Plate heat exchanger



Sept. 3, 1968 H. DOELZ ET AL 3,399,720

PLATE HEAT EXCHANGE-R Filed Sept. 50, 1966 5 Sheets-Sheet 1 mass; l

"8 I u c- E '4- 3 Fig 1 Badman w /fl'kr fheir ATTORNEY Sept. 3, 1968 H.DOELZ ET AL 3,399,720

PLATE HEAT EXCHANGER Filed Sept. 30, 1966 5 Sheets-Sheet 2 fheirATTORNEY p 3, 1968 H. DOELZ ETAL 3,399,720

PLATE HIS AT EXCHANGER Filed Sept. 30, 1966 5 Sheets-Sheet 3 Fig. 3

INVENTORS 28m Alia-6 r Iii f h 15:06,. w J zMM mm, \helr ATTORNEY Sept.3, 1968 DOELZ ET AL 3,399,720

PLATE HEAT EXCHANGER Filed Sept. 30, 1966 5 Sheets-Sheet 4 Fig.4

u INVENTORS Al -w 03A Sept. 3, 1968 H. DOELZ ET AL 3,399,720

PLATE HEAT EXCHANGER Filed Sept. 30, 1966 5 Sheets-Sheet 5 nited StatesPatent 9 3,399,720 PLATE HEAT EXCHANGER Hans Doelz, Halle, EdgarHipperling, Reichenhach, and Joachim Seidel, Mylau, Germany, assignorsto VEB Apparatebau Mylan, Mylau, Plauen, Germany Filed Sept. 30, 1966,Ser. No. 583,405 13 Claims. (Cl. 165166) ABSTRACT OF THE DISCLOSURE Thepresent invention relates to improvements in plate heat exchangers.

It is an important object of the present invention to provide a verycompact, lightweight, rigid and inexpensive plate heat exchanger.

Another object of the invention is to provide a plate heat exchanger ofthe just outlined characteristics whose efliciency at least equals thatof presently known plate heat exchangers and which may be utilized inexisting mechanical refrigerating machines, especially invaporcompression machines.

A further object of the invention is to provide a plate heat exchangerwherein the parts which confine the fluids and thus direct their flowsimultaneously perform the function of stiffeners so that no specialreinforcing parts are needed to lend necessary rigidity to the body ofthe heat exchanger.

An additional object of our invention is to provide a heat exchangerwherein the flow of at least one fluid may be obstructed in a verysimple way to insure more effective exchange of heat with the otherfluid.

A concomitant object of the invention is to provide a plate heatexchanger which may be assembled of very simple components, whosecomponents may be massproduced by resorting to known machinery, whichmay be assembled by resorting to automatic machines so that the numberof manual operations and man hours may be reduced to a minimum, andwhich can be utilized to bring about exchange of heat between fluidswhile such fluids are subjected to elevated pressures.

Briefly stated, one feature of the present invention resides in theprovision of a method of exchanging heat between a cooler fluid and awarmer fluid. The method comprises the steps of conveying the fluidsalong two substantially U-shaped paths one of which surrounds the otherthereof, and separating the paths from each other by relatively thinlayers of heat-conducting material which takes up heat from the warmerfluid and transmits it to the cooler fluid.

The cross-sectional area of the path for cooler fluid is preferablygreater than the cross-sectional area of the path for warmer fluid. Thecooler fluid may be in gaseous state and the warmer fluid may be inliquid state. For

ice

example, and if the method is resorted to in a refrigerating operation,the warmer fluid may be maintained at a temperature approximating roomtemperature.

Each of the two paths may be subdivided into a plurality of narrowerpaths extending in the direction of fluid flow, and such subdivision maybe carried out by inserting into the paths thin layers ofheat-conducting material and by placing such thin layers inheat-conducting contact with the first-mentioned layers. In manyinstances, we prefer to place into one of the paths suitableobstructions which produce turbulence in the respective fluid and thusenhance the exchange of heat between such fluid and the aforementionedlayers.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved heat exchanger itself, however, both as to its construction andthe mode of assembling the same, together with additional features andadvantages thereof, will be best understood upon perusal of thefollowing detailed description of certain specific embodiments withreference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a refrigerating machine comprising aplate-type heat exchanger which embodies the present invention;

FIG. 2 is a greatly enlarged perspective view of the heat exchanger witha corner portion broken away;

FIG. 3 is a longitudinal central vertical section through the heatexchanger, substantially as seen in the direction of arrows from theline IIIIII of FIG. 2;

FIG. 3a is a diagrammatic longitudinal sectional View through apartially assembled heat exchanger which is somewhat different from theheat exchanger of FIGS. 2 and 3;

FIG. 4 is a transverse section substantially as seen in the direction ofarrows from the line IVIV of FIG. 3 and illustrates one mode of bondingthe components of a heat exchanger to each other;

FIG. 5 is a similar transverse section and illustrates another mode ofbonding the parts of a heat exchanger to each other;

FIG. 6 is another transverse section and illustrates a third mode ofbonding the parts of a heat exchanger to each other;

FIG. 7 is a smaller-scale diagrammatic perspective view of a heatexchanger which is constructed in a manner as shown in FIGS. 2 and 3;

FIG. 8 is a diagrammatic perspective view of a battery of two seriallyconnected heat exchangers;

FIG. 9 illustrates in perspective view a battery of three seriallyconnected heat exchangers;

FIG. 10 is a perspective view of an assembly which comprises twobatteries of the type shown in FIG. 8 and wherein the heat exchangers ofthe adjoining batteries are connected in parallel; and

FIG. 11 is a perspective view of a modified assembly comprising twobatteries of three serially connected heat exchangers each.

Referring first to FIG. 1, there is shown a mechanical refrigeratingmachine embodying a plate type heat exchanger 31 which is constructedand assembled in accordance with our invention. The exact constructionof the remaining parts of the refrigerating machine is known and isdescribed here for the sole purpose of fully disclosing oneadvantageousutilization of the improved heat exchanger.

The refrigerating machine of FIG. 1 is a simple vaporcompression machinecomprising a compressor unit 20 which includes a prime mover and acompressor proper, preferably a reciprocating compressor which is drivenby an electric motor. Gaseous refrigerant which is compressed in theunit 20 passes through a discharge valve 21 and a discharge line 22 intothe coils 24 of a condenser unit 23. The coils 24 may be cooled bycurrents of water and/or fresh air. In the present instance, the coilsare cooled by currents of air generated by a fan 27 whichis drven by theoutput shaft 26 of an electric motor. Such currents pass along the fins25 of the coils 24 and the thus liquefied refrigerant is conveyedthrough a conduit 28 and enters a collecting tank 29. A conduit 30conveys liquid refrigerant from the tank 29 and into one duct of theheat exchanger 31. A further conduit 32 conveys liquid refrigerant(which is pressurized by the compressor of the unit 20) to athermostatically controlled expansion valve 33. The heat necessary forevaporation in the expansion coil 35 which receives refrigerant from theoutlet 34 f the expansion valve 33 is withdrawn from the areasurrounding the coil 35. The gasified refrigerant then passes through aconduit 36 and its temperature is measured by a thermostat 37 whichcontrols the expansion valve 33 through a line 38. The conduit 36discharges into a second duct of the heat exchanger 31 (this second ductis indicated diagrammatically as being constituted by the passagedefined by a meandering coil 39), and the second duct admits heatedrefrigerant to a suction conduit 40 connected to a suction valve 41which in turn admits refrigerant into the compressor of the unit 20. Thecycle is then repeated in the just described manner.

In the refrigerating machine of FIG. 1, the heat exchanger 31 performsthe important function of bringing about exchange of heat between thehighly compressed liquid phase admitted by the conduit 30 and thegaseous phase admitted by the conduit 36. The liquid phase which entersthe heat exchanger 31 is warm, i.e., its temperature approximates orslightly exceeds room temperature or the temperature of ambient air inthe plant where the machine is put to use. The gaseous phase which isadmitted by the conduit 36 is cold and this gaseous phase withdraws heatfrom the liquid phase. The cooling effect is improved if the heatexchanger 31 (and more particularly the gaseous phase flowing throughthis heat exchanger) withdraws more heat from the liquid phase which iscompelled to flow toward the expansion valve 33. On the Other hand, andparticularly if the refrigerant is dichlorodifluoromethane (CCl F orsimply Freon 12), heating of the gaseous phase on its way to the suctionside of the compressor in the unit results in improved performance ofthe compressor so that the exchange of heat in the heat exchanger 31 isdesirable for a plurality of reasons. Such exchange of heat between theliquid and gaseous phases of the refrigerant results in substantialsavings in energy and reduces the operating cost of the refrigeratingmachine.

The thermostat 37 measures the temperature of the gaseous phase andregulates the expansion valve 33 in dependency on such temperature,i.e., the valve controls the rate at which the liquid phase is admittedinto the expansion coil 35 to prevent flooding of this coil and eventualadmission of liquefied refrigerant to the suction side of thecompressor.

FIGS. 2 and 3 show the heat exchanger 31 on a greatly enlarged scale andin full detail. This heat exchanger comprises two housings including anouter housing A composed of two mirror symmetrical pan-shaped shells 54,55 and an inner housing B composed of two mirror symmetrical shells 51,52. The two housings define between themselves a first or outer U-shapedduct 56 which serves to convey the warmer fluid, i.e., the liquid phaseof the refrigerant utilized in the machine of FIG. 1. The inner housingB accommodates a plate-like separator 57 which 4 defines therewith asecond or inner U-shaped duct 53 serving to convey the cooler fluid,i.e., the gaseous phase of the refrigerant. The inner duct 53 issurrounded by the outer duct 56 and the relatively thin walls of theinner housing B serve as 'a means for conducting heat from the warmerfluid to the cooler fluid. Since the temperature of the Warmer fluid isnot substantially different from the temperature of the air surroundingthe outer housing A, the exterior of the heat exchanger 31 need not beinsulated when the latter is used in a refrigerating machine of the typeshown in FIG. 1. The separator 57 is disposed in the central symmetryplane of the heat exchanger.

The exact configuration of the ducts in the interior of the heatexchanger 31 will be more readily understood by referring shortly toFIG. 3a which shows, very diagrammatically, one mode of forming a heatexchanger similar to that illustrated in FIGS. 2 and 3. One can startwith a plate-like separator 301, with a first pan-shaped shell 302 whoseopen side is adjacent to the upper side of the separator 301, and with asecond pan-shaped shell 303. By bending the structure of FIG. 311 aboutan axis 304 extending transversely of the separator 301, one wouldobtain a heat exchanger which is similar to the heat exchanger 31 ofFIGS. 2 and 3. The space 310 between the separator 301 and the innershell 302 would form an inner duct corresponding to the duct 53 and thespace 311 between the shells 302, 303 would form an outer ductcorresponding to the duct 56. Pipes 306, 307 would respectively admitand evacuate one phase from the space 311 and pipes 308, 309 wouldrespectively admit and evacuate the other phase from the space 310.

However, and since the production of the heat exchanger is simplfied ifthe bending step of FIG. 3a is dispensed with, we prefer to assemble theheat exchanger 31 in a manner as outlined in connection with FIGS. 2 and3, namely, by assembling each of the housings A and B of two separateshells (54, 55 and 51, 52) and by utilizing a separator 57 which neednot be bent over itself.

Referring now again to FIGS. 2 and 3, the upper shell 54 of the outerhousing A comprises a bottom wall or panel 54a of rectangular outline,two longitudinally extending side walls 54b, 54c and two transverselyextending side walls 54d, 54c. Where shown, the corresponding walls ofthe other three shells 55, 51 and 52 are respectively denoted by similarreference numerals 55a55e, Sla-Sle and 52a52e. The side walls 51b51e,52b-52e, 54b-54e and 55b55e are respectively provided with outwardlyextending marginal portions or flanges 51 52 54f and 55 which areassembled into a package whereby the flanges 51f, 52f abut against theopposite sides of the marginal portions of the separator 57. Inaddition, the flanges 55f of the lower shell 55 are bent over theflanges 54 of the upper shell 54, as shown at 55g, so as to fullyconceal the flanges 51 52 54f and to form a continuous annular beadaround the separator 57. The manner in which the flanges 51 52 54f, 55are sealingly bonded to each other will be described in connection withFIGS. 4 to 6. It will be noted that the bentover portions 55g of theflanges 55] by themselves maintain the four shells 51, 52, 54 and 55 andthe separator 57 in assembled condition.

The separator 57 has an opening or cutout 57a which is located in acentral or median zone or portion 530 of the inner duct 53 and isadjacent to the side walls 510, 52s. This separator 57 is also providedwith a second opening or cutout 57b which is located in the central ormedian portion or zone 560 of the outer channel 56 and is adjacent tothe side walls 542, 552. The opening 57!) registers with openings orcuts out 51h, 5211 provided in the flanges 51f, 52) of the side walls51c, 52a.

The opening 5212 is formed by bending from the plane of the flange 52 aflap 52g which extends through the registering openings 57b, 5111 and isbent over the adjoining portion of the flange 51 to form a bead whichholds the parts 51c, 52c and 57 together.

The two elongated portions or the inner duct 53 which extend along theinner sides of the bottom walls 51a, 52a and along the adjoining sidesof the separator 57 accommodate elongated fins 58 of thinheat-conducting ductile material which divide the corresponding portionsof the ducts 53 into a number of narrower passages 0r ducts 53a clearlyshown in FIG. 2. Such panels 58a of the fins 58 which extend between thebottom walls 51a, 52a and the separator 57 are preferably bent back andforth to form sharply defined pockets 58b. Undulate fins 59 of thinheat-conducting ductile material are inserted between such portions ofthe outer duct 56 which extend between the bottom walls 51a, 54a and52a, 55a to form narrower ducts or passages 56a. The passages 53a, 56aextend in the direction of fluid flow through the ducts 53, 56.

The specific configuration of the panels of the fins 58 products in theduct 53 a certain turbulence which enhances the exchange of heat betweenthe two fluids. The pockets 581) are preferably provided at regularintervals and the pockets in the upper arm of the duct 53 may but neednot be accurately aligned with the pockets in the lower arm.

The fins 58 and 59 are shorter than the bottom walls 510, 52a and 54a,55a so that the leftmost portions of the ducts (as viewed in FIG. 3) arefree of such fins. These portions of the ducts 53, 56 are respectivelyconnected with fluid admitting pipes 64, 68 and with fluid evacuatingpipes 65, 69. The bottom walls 51a, 52a, 54a, 55a are respectivelyprovided with outwardly extending annular sockets 60, 61, 62, 63 whichreceive the ends of pipes 64, 65 in a manner best shown in FIG. 3. Thebottom walls 54a, 55a are provided with additional sockets 66, 67 whichreceive the end portions of the pipes 68, 69. The fins 59 in the outerduct 56 preferably extend between the inner end portions of the pipes68, 69 and the side walls 51e, 52e, and the fins 58 preferably extendbetween the inner end portions of the pipes 64, 65 and short of the sidewalls 51e, 52e so that they leave at least a portion of the opening 57ain the separator 57 exposed. As shown in FIG. 3, fluid entering theouter duct 56 via pipe 68 and leaving via pipe 69 flows in the samedirection as the fluid which enters the duct 53 via pipe 64 and leavesvia pipe 65. Thus, all of the pipes 64, 65 and 68, 69 can be installedat one and the same longitudinal end of the heat exchanger. The endfaces of the sockets 60, 62 and 61, 63 are preferably located in commonplanes so that the gaps between such pairs of concentric sockets can bereadily sealed to prevent communication of the duct 56 with thesurrounding atmosphere. The inner end portions of the pipes 64, 65, 68,69 are bounded by end faces which are inclined in a. manner as clearlyshown in FIG. 3. Thus, the inner end faces of the pipes 64, 65respectively extend from the separator 57 to the bottom walls 51a, 52a,and the inner end faces of the pipes 68, 69 respectively extend from thebottom walls 51a, 52a to the bottom walls 54a, 55a. Such inclination oftheir inner end faces enables the pipes 64, 68 to automatically directfluids toward the intake ends of the upper passages 53a, 56a whereas theintake ends of the pipes 65, 69 face the discharge ends of the lowerpassages 53a, 56a. The end zones of the ducts 53, 56 which are free offins 58, 59 and which respectively accommodate the inner end portions ofthe pipes 64, 65 and 68, 69 are respectively denoted by referencenumerals 53b and 56b. The upper zones 53b, 56b can be calleddistributing compartments because they distribute fluids admitted by thepipes 64, 68 into the passages 53a, 56a. The lower zones 53b, 56b can becalled collecting compartments because they receive fluid streams fromthe lower passages 53a, 56a and their contents can be evacuated viapipes 65, 69.

The cross-sectional area of the outer duct 56 is smaller than thecross-sectional area of the inner duct 53. This is due to the fact thatthe heat exchanger 31 of FIGS. 2

and 3 has been shown as having a form which is especially satisfactoryfor use in a refrigerating machine wherein the volume of the gas flowingthrough the duct 53 is a multiple of the volume of the liquid passingthrough the duct 56. The ratio of the two volumes may be as high as200:1. This must be borne in mind in designing and assembling a platetype heat exchanger for use in refrigerating machines, i.e., it willhave a bearing upon the relationship between the size and weight on theone hand and the efliciency of the heat exchanger on the other hand.

The feature that the outer U-shaped duct 56 surrounds the inner U-shapedduct 53 contributes to the compactness of our improved heat exchanger.It is also novel to convey the liquid phase in the outer duct 56 so thatthe outer housing A need not be insulated at all if the temperature ofthe liquid phase approximates the temperature of surrounding air. In arefrigerating machine of the type shown in FIG. 1, the temperature ofthe liquid phase will range between 35-40 C.

Another very important advantage of the heat-exchanger 31 is that itoffers unexpectedly high resistance to deformation despite the fact thatits components may and preferably consist of thin sheet or plate stock.This is attributed to the utilization of pan-shaped shells 51, 52, 54,55. Of course, the exchange of heat between the two phases is moresatisfactory if the walls of the shells 51, 52 and of the separator 57are thin, and the utilization of thin plate or sheet stock renders itpossible to produce a heat exchanger of surprisingly low weight.

Various modes of connecting the shells of the heat exchanger 31 to eachother and with the fins 58, 59 and separator 57 are illustrated in FIGS.4, 5 and 6. These parts are preferably connected to each other bybonding, for example, by soldering or brazing.

FIG. 4 illustrates length of copper wire 70 which are inserted in allsuch areas where the material of such wire should form fluidtight jointsbetween the fins 58, 59 and the parts 57, 51a, 52a, 54a, 55a and alsobetween the flanges 51], 52 54f, 55 and separator 57. The distributionof wires 70 is preferably such that, during melting, their materialforms uniform seams along all such portions which are to be bonded toeach other. As shown, wires 70 are inserted into the passages 53a, 56aand also along the exposed end face of the outer bead 55g. Duringheating, the heat exchanger 31 is preferably held in a position in whichone longitudinally extending portion of the bead 55g rests on a suitablesupport.

FIG. 5 illustrates another mode of bonding the various parts of a heatexchanger 31 to each other. In this embodiment of the invention, thewires 70 of FIG. 4 are replaced by foils 71 which coat both sides of theseparator 57, both sides of each of the inner shells 51 52, and theinner sides of the outer shells 54, 55. Portions of the foils 71 extendbetween the adjoining flanges 51 52 54], 55 as well as between suchflanges and the marginal portions of the separator 57 so that even theflanges are bonded to each other and to the separator.

It is also possible to utilize shorter or narrower sheets or foils 72(see FIG. 6) and to utilize some wires 70 whereby the foils 72 bond thefins 58, 59 to the bottom walls 51a, 52a, 54a, 55a and to the separator57 whereas the wires 70 form seams which provide fluidtight seals alongthe exposed end face of the bead 55g. The method illustrated in FIG. 6requires more work but the savings in foil stock are considerable.

Though not shown in FIGS. 4 to 6, the sockets 60-63 and 6667 are alsosoldered or brazed to the pipes 64, 65 and 68, 69 to prevent leakage.Such bonding operation can be carried out by placing rings of wire 70along these sockets. The sockets may be formed with annular ribs (notshown) which extend into complementary annular grooves of the adjoiningpipes, and the wires 70 may be forced into such grooves to insure that,after heating and subsequent cooling, the material of such wires willinvariably form fluidtight seals around the pipes. Alternatively, theend portions of the pipes 64, 65, 68, 69 may have smaller diameters thanthe remainder of such pipes so that each pipe develops an annularshoulder which is placed adjacent to a ring of copper wire abuttingagainst the respective socket or sockets to insure the formation ofcircumferentially complete annular seams. Such rings of copper wire canbe clamped in position up to the time when their material is fused inresponse to heating in a soldering furnace.

Referring finally to FIGS. 8 to 11, there are shown several possiblecombinations of two or more heat exchangers 31 of the type schematicallyillustrated in FIG. 7. In FIG. 8, two heat exchangers 31 are assembledto form a battery of serially connected components whereby the fluidevacuating pipes 65, 69 of the upper heat exchanger extend into andconstitute the fluid admitting pipes for the lower heat exchanger. Thelower ends of the pipes 65, 69 of the upper heat exchanger arepreferably provided with inclined end faces as illustrated in FIG. 3.The common pipes 65, 69 of the two heat exchangers may be very short sothat the heat exchangers can be located in two closely adjacent planes.The free ends of the pipes 64, 68 and 65, 69 are coupled with suitableflexible or rigid conduits (not shown) which connect the battery intothe machine of FIG. 1 or into another machine where the heat exchangersare being used.

FIG. 9 shows a battery of three serially connected heat exchangers 31which form a single file whereby only the uppermost heat exchangercomprises four pipes 64, 68, 65, 69.

If the heat exchangers 31 are disposed in two or more rows, for examplein two rows each of which comprises two serially connected heatexchangers 31 in a manner as illustrated in FIG. 10, the adjoining heatexchangers in the two rows have their fluid admitting pipes 64, 68connected by h aders 73, 74 which receive fluids through supply conduits77, 78. The fluid evacuating pipes 65, 69 of the two lower heatexchangers 31 are connected with headers 75, 76 having dischargeconduits 79, 80. It will be seen that the heat exchangers of one row areconnected in parallel with the heat exchangers of the other row.

FIG. 11 illustrates an assembly of six heat exchangers 31 disposed intwo rows of three serially connected heat exchangers each. Such anassembly is obtained by introducing into the assembly of FIG. twointermediate heat exchangers.

It is further clear that the heat exchangers 31 may be assembled intobatteries which comprise three or more rows or into batteries comprisingfour, five or more heat exchangers disposed in a single row.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention, that others can, by applying current knowledge,readily adapt it for 'various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. A plate-type heat exchanger comprising an outer housing and an innerhousing received in said outer housing and defining therewith a U-shapedouter duct having a pair of legs for passage of a first fluidtherethrough, each of said housings comprising a pair of substantiallypanshaped shells having marginal portions sealingly secured to eachother; separator means installed in and defining with said inner housinga second U-s'haped duct having a pair of second legs for passage of asecond fluid therethrough whose temperature is different from that ofthe first fluid, said separator means having marginal portions receivedbetween said marginal portions of said housing and being formed in theregion of one end of said heat exchanger with a pair of openings, onelocated in said outer housing and providing communication between saidpair of first legs and the other being located in said inner housing andproviding communication between said pair of second legs, said innerhousing consisting of heat conductive material to provide for heatexchange between said fluids; a first pair of passages communicatingrespectively with said first pair of legs in the region of the other endof said heat exchanger for respectively feeding said first fluid int-oone end of one of said first pair of legs and for discharging the firstfluid from the corresponding end of the other of said pair of firstlegs; and a second pair of passages communicating respectively with saidpair of second legs in the region of said other end of saidheat-exchanger for respectively feeding said second fluid into one endof one of said pair of second legs and for discharging the first fluidfrom the corresponding end of the other of said pair of second legs.

2. A heatexchanger as set forth in claim 1, wherein each of saidpan-shaped shells has a substantially flat bottom wall extendingsubstantially parallel to said separator means, and wherein saidpassages are formed by pipes extending substantially normal to saidbottom walls.

3. A heat exchanger as set forth in claim 2, wherein said bottom wallsare provided with sockets integrally formed therewith and wherein saidpipes extend with end portions thereof through said sockets sealinglyconnected thereto.

4. A heat exchanger as set forth in claim 3, wherein the pipes formingsaid first pair of passages and the pipes forming said second pair ofpassages are respectively coaxially arranged.

5. A heat exchanger as set forth in claim 4, wherein said bottom wallsof said shells forming said outer housing are each formed with a pair ofsaid sockets projecting outwardly from the respective wall and whereinsaid sockets formed in said bottom walls of said shell forming saidinner housing respectively project through one of said pair of socketsin the corresponding outer shell and being sealingly connected thereto.

6. A heat-exchanger as set forth in claim 1, wherein said marginalportions of said shells are constituted by outwardy extending rimportions, and wherein one of said pair of shells forming said outerhousing has a rim portion which is wider than the other rim portion ofsaid pair and is folded over said other rim portion to secure said rimportions to each other.

7. A heat-exchanger as set forth in claim 6, wherein said rim portionsof the shells forming said inner housing are sandwiched between said rimportions of the shells forming said outer housing, and wherein said oneopening extends also through said rim portions of said inner shells.

8. A heat-exchanger as set forth in claim 7, wherein part of the trimportion of one shell forming said inner housing extends through said oneopening and is folded over a corresponding part of the rim portion ofthe other shell forming said inner housing.

9. A heat exchanger as set forth in claim 1, further comprising finsprovided in each of said ducts and subdividing the respective ducts intoplural passages extending in the direction of fluid flow through saidducts.

10. A heat exchanger as set forth in claim 9, wherein the fins in one ofsaid ducts are provided with flow obstructing portions to generateturbulence in the respective fluid.

11. A heat exchanger as set forth in claim 1, wherein said separatormeans comprises a panel disposed in a predetermined plane and whereineach of said housings comprises two halves which are substantiallymirror symmetrical with reference to such plane.

3,399,720 9 1O 12. A heat exchanger as set forth in claim 3, whereinReferences Cited the end portions of said pipes are bounded by end facesUNITED STATES PATENTS located in planes which make acute angles with theaxes of the respective pipes 2,571,631 10/1951 Trumpler 165-166 :13, Aheat exchanger as set forth in claim 1, further 5 2940736 6/1960 O1man165 166 comprising fins provided in each of said ducts and sub- 2979,310 4/1961 Nlcholson 165141 dividing the respective ducts into pluralpassages extend- FOREIGN PATENTS ing in the direction of fluid flowthrough such ducts, each 25 687 12/1899 Great Britain of said ductscomprising a pair of elongated portions which accommodate the respectivefins and a median 10 ROBERT OLEARY Primwy Examiner. portion free of finsand connecting the respective longer portions CHARLES SUKALO, AsszstantExammer.

